Faculty of Engineering

NEAR EAST UNIVERSITY

Faculty of Engineering

Department of Electrical and Electronic

Engineering

SIM CARD

Graduation Project

EE· 400

Student:

Shaban Jbarah (990969)

Supervisor:

Mr Jamal Abu Hasna

••

.,.

••

Initially I would like to thank Mr Jamal Abu Hasna for being my adviser actually I could overcome many difficulties successfully under his guidance .He always helps me either in my graduation project or during my studying period .

All of my thanks to Mr Ozgur Ozerdem who explained a lot of points for my project regulation .

Finally I would like to thank my family who support me in learning field especially my parents . Without their endless support and love , I would never achieve my current position . I wish them lives happy life .

ABSTRACT

The SIM Card becoıne so important in our life, cause of it can be useful ın our life orders ; it has many uses which it can make the life more easier .

The main objective of this thesis is to provide analysis and systematisation of the SIM Card .especiallythat one which uses for cell phone .

For this Purpose We need a program which can discover the contents of SIM Cards .to full understand how the operation of SIM card accomplish. The underling principle of reconstruction the program to do what we need in the SIM Card through reader and writer devise .

ACKNOWLEDGMENT , .

AB·STRACT - , ,..

INTRODUCTI ...•...

L CELLULAR COMMUNICATIONS .

1. I. Definition .

1. 1 .1. Cellular Mobile Communication .

1.1.2. Global System for Mobile Communication (GSM) .

1.2. Mobile Communications Principles .

1.3. Early Mobile Telephone System Architecture .

1.4.Mobile Telephone System Using the Cellular Concept ...•...

I .5. Cellular System Architecture .

1.5.2. Clusters .

1.5.3. Frequency Reuse .

1.5.4. Cell Splitting .

1.5.5. Handoff , .

1 .6. North American Analog Cellular Systems .

1.6.1. The Advanced Mobile Phone Service (AMPS) .

1.6.2. Narrowband Analog Mobile Phone Service (NAMPS) .

I. 7. Cellular System Components .

1.7.1. PSTN •••••••••••••••••••••••••••••••• "'••••••••••••••••••• "'•••• '•••• '! ••••

1. 7.2. Mobile Telephone Switching Office (MTSO) .

1.7.3. The Cell Site .

l.7.4. Mobile Subscriber Units (MSUs) .

1.8. Digital Systems ...•...•...

1.8.1. Time Division Multiple Access (TDMA) .

I .8.2. Extended Time Division Multiple Access (E-TDMA) .

1.~.3. Fixed Wireless Access (FWA) .

1.8.4. Personal Communications Service (PCS) .

1.8.5. Code Division Multiple Access (CDMA) .

2.1 HOW CELL PHONES WORl(S •...•....•...•.••...•...

2.1. Introduction . ~ , ' .

2.2. The Cell Approach , .

2.3. Cell Phones Codes .

2.4. From Cell To Cell ...•... ~· .

2.5. Roaming ~ , .

2.6. Cell Phone And CBS .

2.7. Advance Mobile Phone System (AMPS) .

2.8. Analog Comes Digital .

2.9. Cellular Access Technologies , .

2.9.1. Frequency Division Multiple Access (FDMA) ~· .

2.9.2. Time Division Multiple Access (TDMA) .

2.9.3. Code Divisiort Multiple Access (CDMA) .

2. 10. The Difference Between Cellular And PCs .

2.11. Dual Band And Dual Mode .

2. l 2. Problems With Cell Phones .

2. 13. Inside A Cell Phone .

2.14. Cell Phones Tower , .

I 11 iii 1 1 1 l 1 2 3 4 5 5 6 7 9 9 10 11 11 11 11 12 12 15 15 16 16 17 18 18 18 20 21

22

22 24 24 25 25 26 27 28 29 30 30 34

2.15. What They Can Do . 2.16. Features : , , . 2.16.1. Service Plan . 2.16.2. Mode . 2.16.3. Battery Type ...•... 2.16.4. Display · · · . 2.16.5. Include Function ...•... , . 2.16.6. Special Features .

3. SIM CARD

.

3 .1. Introduction ...•...

3 .2. Smart card functions •... , , . 3.3. Smart card standards and platforms , .

3 .4. Alternatives to smart cards , .

3.5. Contact, Contactless and combi interfaces SIM Card . 3.5.1. Contact smart cards 1 •••••••••••••••••••••

3.5.2. Contactless smart cards .

3.6. Access the information .

3.6.1. Passwords .

3.6.2. Authenticating the cardholder . 3.7. Smart Cards in Wireless Communications .

3.7.1. General .

3.7.2. Enhanced Security Benefits .

3.7.3. Easing Logistical Issues .

3.7.4. Providing Value-Added Services .

3.8. Marketing Opportunities .

3.8.1. Brand Recognition .

3.8.2. Customer Loyalty Programs .

3.8.3. Direct Marketing •...

3.8.4. Advertising .

3.8.5. Trial Subscriptions .

3.8.6. Incidental Revenues .

3.9. User Benefits .

3.9.1. Full Portability of Services ...•...

3.9.2. International Roa~~ .

3.93.Intersystem Roamıng .

3.9.4. Multiple Services on a Single Card . 3.9.5. Separation of Business and Personal Calls . 3.10. Factors Driving Smart-Card Acceptance : . 3.10.1. Industries and Institutions , . 3.10.2. Consumers Primed to Use Smart Cards .

4. SIM CARD

&

GSM SECURITY

.

4.1. Security Of SIM Card .

4.2, GSM System Security .

4.2.1. Overview ofGSM Security Features . 4.;ı.2. Subscriber Identity Authentication . 4.2.3. User and Signalling Data Confidentiality . 4.2.3. Subscriber Identity Confidentiality . 4.3. The French Proposal for the Cipher . 4.3.1. PDL Description of the Cipher , .

4.3.2 the Shift Function f .

36 37 37 38 38 38 39 39 40 40 41 42 43 43 44 44 45 45 46 47 47 48 49 50 51 52 52 52 53 53 54 54 54 54 55 55 56 56 56 57 58 58 59 59 59 61 62 63 63 64

4.3.5 Performing the Shifts . . . 66 4.3.6. Hardware Estimates .. . . .. . . 69 4.3.6. Hardware Estimates 70 4.3..8. Shift Function f , . . . .. 71 4.3.9 Speed Estimates , . . . 73 CONCLUSION ... .. . .. . .. . . .. .. . ... . .. .. . . .. . ... .... .. . . .. . .. . . ... . . 7,4 REFERENCES

···•···ıı···•···

75

•

INTRODUCTION

Millions of people around of the world are using cellular :phones. They are such great gadgets with a cell phone; you can talk to any one on the planet from just about anywhere.

Since every one agree with the importance of a cell phone, I have prepared this

,

project to be in the hand of student and professional as will, and to make it easy I have put into three chapters.

In the chapter one I briefly present the concept of cellular communication and discuss the first-and s~ond- generation cellular systems used in the Northern ofUnited States and Europe. I out line the problems associated with the Cellular Communication system and provide the vision of a third-generation system.

In the chapter two, I present how cell phone works? And I have discussed the cell approach and cell phones codes, and what makes it different from a regular phone? What do al these confusing terms like PCS, GSM, CDMA and TDMA mean? Also I have described the technology behind call phones.

In the chapter three I present a SIM Card, SIM Card application , advantage and the types either contact smart card or contactless smart cards and the compound one . I have described the architecture of it, security of smart cards ,Authenticating the cardholder, Passwords, access the information.

In Chapter four I research for technology and structure of smartcards ,signaling data of sim card, spectrum efficiency and logical channel which has described logical categories, blocks codes, logical channel formats.

Understanding the security of GSM "mobile phone through the SIM card and separately , network security , PDL Description of the Cipher , function öf security and a]gorimths , etc.

1~ CELLULAR COMMUNICATIONS

1.1 Definition

1.1.1. Cellular Mobile Communication

A cellular mobile communications system uses a large number of low-power ,ireless transmitters to create cells-the basic geographic service area of a, wireless communications-system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from

cell to cell, their conversations are handed off between cells to maintain seamless

service. Channels (frequencies) used in one cell can be reused in another cell some

disıance away. Cells can be added to accommodate growth, creating new cells in unserved areas or overlaying cells in existing areas.

1.1.2. Global

System

for Mobile Communication (GSM)

It is a globally accepted standard for digital cellular communication. GSM is the

name of a standardization group established in 1982 to create a common European bile telephone standard that would formulate specifications for a pan-European ,biJe cellular radio system operating at 900 MHz. It is estimated that many countries

OQ(sic:Je of Europe willjoin the OSM partnership.

Mobile

Communicatioas

Principles

Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell

"

to many mobiles at once, using one channel per mobile. Channels use a pair of .hquencies for communication--one frequency for transmitting from the cell site and

frequency for the cell site to receive calls from the users. Radio energy dissipates distance, so mobiles must ştay near the base station to maintain communications. · structure of mobile networks includes telephone systems and radio services• .,_,,. mobile radio service operates in

a

closed network and has no access to the

• • ınme

system, mobile telephone service allows interconnection to the telephone

Cellular Communication ·. Mobile Base Station Mobile Base Station Mobile Control Equipment Network Interface Equipment ·~ ,r ••~

Figure 1.1 Basic Mobile Telephone Service Network

.3. Early Mobile Telephone

System

Architecture

Traditional mobile service was structured in a fashion similar to television

.··r

moadcasting: One very powerful transmitter located at the highest spot in an area would moadcast in a radius of up to 50 kilometers. The cellular concept structured the mobile

~

ıdq,hone network in a different way. Instead of using one powerful transmitter, many '

r-power transmitters were placed throughout a coverage area. For example, by

•

dn..Ylino a metropolitan region into one hundred different areas (cells) with low-power

baısmitters using 12 conversations (channels) each, the system capacity theoretically be increased froın 12 conversations=-or voice channels using one powerful b:a&oitter-to 1,200 conversations (channels) using one hundred. low-power baıısmitters . Figure1 .2 shows a metropolitan area configured as a traditional mobile

,

Figuret.2 Early Mobile Telephone System Architecture

1.4. Mobile Telephone System Using the Cellular Concept

Interference problems caused by mobile units using the same channel in adjacent areas proved that all channels could not be reused in every cell. Areas had to be skipped fore the same channel could be reused. Even though this affected the efficiencyof the original concept, frequency reuse was still a viable solution to the problems of mobile telephony systems.

Engineers discovered that the interference effects were not due to the distance between areas, but to the ratio of the distance between areas to the transmitter power radius) of the areas. By reducing the radius of an area by 50 percent, service providers could increase the number of potential customers in an area fourfold. Systems based on areas with a one-kilometer radius would have one hundred times more channels than ems with areas 1 O kilometers in radius. Speculation led to the conclusion that by reducing the radius of areas to a few hundred meters, millionsof calls could be served.

'

The cellular concept employs variable low-power levels, which allow cells to be sized according to the subscriber density and demand of a given area. As the population grows, cells can be added to accommodate that growth. Frequencies used in one cell cluster can be reused in other cells. Conversations can be handed off from cell to cell to mıintain constant phone service as the user moves between cells (Figure 1.3).

Cellular Communication

. :·:----.--:~· .. . . . .

Figure 1.3 Mobile Telephone System Using a Cellular Architecture

..

. 1, ~-f

I _{Cellular System Architecture}

..;;,;_',J·'

Increases in demand and the poor quality of existing service led mobile service to research ways to improve the quality of service and to support more users · systems. Because the amount of frequency spectrum available for mobile

cdular use was limited, efficient use of the required frequencies was needed for mobile

a..cwucır coverage. In modern cellular telephony, rural and urban regions are divided into

according to specific provisioning guidelines. Deployment parameters, such as of cell-splitting and cell sizes, are determined by engineers experienced in

a:lkılar system architecture.

Provisioning for each region is planned according to an engineering plan that

includes cells, clusters, :frequencyreuse, and handovers.

~ t· •• ... ·.•·

.

' ,. ,.} ,r ı:ı

•

,_!' •• , /;1 1. Cells

A cell is the basic geographic unit of a cellular system. The term cellular comes from ,neycomb shape of the areas into which a coverage region is divided. Cells are stations transmitting over small geographic areas that are represented as hexagons.

cell size varies depending on the landscape. Because of constraints imposed by

mturaJ.terrain and man-made structures, the true shape of cells is not a perfect hexagon.

'!·.: \ ı

1.5.2. Clusters

A cluster is a group of cells. No channels are reused within a cluster. Figure 1 .4 ,ımrl-.ıtesa seven-cell cluster.

Cluster size

is exp:ressed as

n

In this cluster n=7

FigurePl.4 A Seven-Cell Cluster

•

Because only a small number of radio channel :frequencieswere available for mobile sysıc:ım., engineers had to find a way to reuse radio channels to carry more than one

CIOD\idsatİon at a time. The solution the industry adopted was called :frequencyplanning

.lrequency reuse. Frequency reuse was implemented by restructuring the mobile

•• ıı:r.nnesystem architecture into the cellular concept.

concept of frequency reuse is based on assigning to each cell a group of radio

,,. '. ~ ~i' ·' ·' ~· .-.. :ı:,T ~·.~· t ,I• T . ;' ,'f' •!,' ' •• 4~;!t ~. ~, Cellular Communication

footprint. This footprint is limited by a boundary so that the same group of channels be used in different cells that are far enough away from each other so that their ftqUeneies do not interfere ( Figurel.S).

Figure \.5 Frequency Reuse

Cells with the same number have the same set of frequencies. Here, because the

-·•er

of available frequencies is 7, the frequency reuse factor is 1/7. That is, each cell

1/7 of available cellular channels.

.. Cell Splitting

nfortunately, economic considerations made' the concept of creating full systems

•

many small areas impractical. To overcome" this difficulty, system operators iek>ped the idea of cell splitting. As a service area becomes full of users, this

ııı,proach is used to split a single area into smaller ones. In this way, urban centers can

into as many areas as necessary to provide acceptable service levels in heavy­ regions, while larger, less expensive cells

can

be used to cover remote rural · ns (Figure 1.6).

Figure 1.6 Cell Splitting

Band off

final obstacle in the development of the cellular network involved the problem

cıaıed when a mobile subscriber traveled from 011e cell to another during a call. As

lj enı areas do not use the same radio channels, a call must either be dropped or • si--ııed from one radio channel to another when a user crosses the line between

Fi :eot cells. Because dropping the call is unacceptable, the process of handoff was

o- Med Hando:ff occurs when the network automatically transfers a call from radio

+ kaıel to radio channel as a mobile crosses adjacent cells as( Figure 1. 7) .

Cellular Communication I - - - l I t I

ellular Switch:

DMS-MTX I

______

, Trunk Routes

Figure 1.7 Handoffbetween Adjacent Cells

' ',-.·:.

During a call, two parties are on one voice channel. When the mobile unit moves out

coverage area of a given cell site, the reception becomes weak. At this point, the

site in use requests a handoff. The system switches the call to a stronger-frequency

-h+ıcl in a new site without interrupting the call or alerting the user. The call wiıııes as long as the user is talking, and the user does not notice the handoff at all.

.

.

,

1.6. North American Analog Cellular

Systems

Originally devised in the late 1970s to early 1980s, analog systems have been revised somewhat since that time and operate in the 800-MHz range. A group of

vernment, telco, and equipment manufacturers worked together as a committee to elop a set of rules (protocols) that govern how cellular subscriber units (mobiles) communicate with the cellular system. System development takes into consideration

different, and often opposing, requirements for the system, and often

a

rnmnromise between conflicting requirements results. Cellular development involves

following basic topics:

of radio modulation

processing sequences

;v,'.,ır;,_,. 1. The Advanced Mobile Phone Service (AMPS)

AMPS was released in 1983 using the 800-MHz to 900-MHz frequency band and kHz bandwidth for each chehnel as a fully automated mobile telephone service. the first standardized cellular service in the world and is currently the most

•

_ used standard for cellular communications. Designed for use in cities, AMPS exoanded to rural areas. It maximized the cellular concept of frequency reuse by h •q.! radio power output. The AMPS telephones (or handsets) have the familiar •lıiil-ıoe-style user interface and are compatible with any AMPS base station. This mobility between service providers (roaming) simpler for subscribers.

,- -P•iı,os associated with AMPS include the following:

Cellular Communication

room for spectrum growth

,rdata communications

- ,imalprivacy

te fraud protection

&\£PS is used throughout the world and is particularly popular in the United States, America, China, and Australia. AMPS uses frequency modulation (FM) for radio •-woission. In the United States, transmissions from mobile to cell site use separate

IDpeucies from the base station to the mobile subscriber.

arrowband Analog Mobile Phone Service (NAMPS)

'

analog cellular was developed, systems have been implemented extensively

• -.bout the world as first-generation cellular technology. In the second generation of

_.,.,.,...,g

cellular systems, NAMPS was designed to solve the problem of low calling

ı:aı-:::ity. NAMPS is now operational in 35 U.S. and overseas markets, and NAMPS

nroduced as an interim solution to capacity problems. NAMPS is a U.S. cellular system that combines existing voice processing with digital signaling, tripling the

eıı,«iıy of today's AMPS systems. The NAMPS concept uses :frequencydivision to get

- MııeJs in the AMPS 30-kHz single channel bandwidth. NAMPS provides 3 users in

channel by dividing the 30-kHz AMPS bandwidth into 3 1 O-kHz channels.

&:reases the possibility of interference because channel bandwidth is reduced.

" ~ ~ ıi j ;'_! ' •::. '·· '/i.,, ·..ı.' .. . • ~.:· ;ı1ı. ..•!! .~,_{.; ..,} 1··t:t.•,r···\'''! •...·,,, r , ı' 1·,~·,'_J ·,", •.~: ;_'· ,. h'~ ')

. Cellular System Components

The cellular system offers mobile and portable telephone stations the same service

a

uided fixed stations over conventional wired loops. It has the capacity to serve tens

-,u:smıus of subscribers in a major metropolitan area. The cellular communications

J o consists of the following four major components that work together to provide

a I 7 service to subscribers.

acaletelephone switching office (MTSO) with antenna system

-•• subscriber unit (MSU)

PSTN

PSTN is made up of local networks, the exchange area networks, and the long­ ork that interconnect telephones and other communication devices on a

1llldlwide basis.

obile Telephone Switching Office (MTSO)

MTSO is the central office for mobile switching. It houses the mobile switching C), field monitoring, and relay stations for switching calls from cell sites to

- iıw central offices (PSTN). I~ analog cellular networks, the MSC controls the

J ı operation. The MSC controls calls, tracks billing information, and locates

7 I subscribers. "

•

The Cell Site

term cell site is used to refer to the physical location of radio equipment that

wides coverage within a cell. A list of hardware located at a cell site includes power

Cellular Communication

',.

.4. Mobile Subscriber Units (MSUs)

The mobile subscriber unit consists of a control unit and a transceiver that transmits receives radio transmissions to and from a cell site. The following three types of

s are available:

mobile telephone (typical transmit power is 4.0 watts) portable (typical transmit power is 0.6 watts)

transportable (typical transmit power is 1 .6 watts)

11ıe mobile telephone is installed in the trunk of a car, and the handset is installed in

renient location to the driver. Portable and transportable telephones are hand-held ean be used anywhere. The use of portable and transportable telephones is limited

charge life of the internal battery.

Digital

Systems

demand for mobile telephone service has increased, service providers found that engineering assumptions borrowed from wireline (landline) networks did not hold · mobile systems. While the average landline phone call lasts at least 1 O minutes,

-ıw

calls usually run 90 seconds. Engineers who expected to assign 50 or more

-ı.e

phones to the same radio channel found that by doing so they increased the that a user would not get dial tone-this is known as call-blocking ııııtıabilitY. As a consequence, thl early systems quickly became saturated, and the

...-ıy

of service decreased rapidly. The critical 'problem was capacity. The general

•

dııncteristics of time division multiple access (TOMA), Global System for Mobile

C ıınications (GSM), personal communications service (PCS) 1900, and code I • --ı multiple access (CDMA) promise to significantly increase the efficiency of

7 7 telephone systems to allow a greater number of simultaneous conversations. .8 shows the components of a typical digital cellular system.

wave Fiber optic

''

Digital Switch

Interfac

Radio controller

:·,:: Figure 1.8 Digital Cellular System

ranıages of digital cellular technologies over analog cellular networks include

- ••: ı:1 capacity and security, Technology options such as TDMA and CDMA offer

ctıanoels in the same analog cellular bandwidth and encrypted voice and data. D : of the enormous amount of money that service providers have invested in

tırs

hardware and software, providers look for a migration from AMPS to digital bile phone service (DAMPS) by overlaying their existing networks with :hitectures(Table1.1 ).

•

"' r.\fr-\fr-.\/r, V/\V/\V/\V Radios

•

Antenna

...

,...,,.{. I·"..1•. ~-' •j :f' . • • .~..., •.:,·-~. ıı.'. ıtf', .,··!, ,.••

'·.

,

..

·-~··, \ 'I," ~' Cellular Communication

Table 1.1 AMPS/DAMPS Comparison

Analog Digital

standard EIA-553 (AMPS) IS-54 (TDMA

+

AMPS)

I spectrum 824 MHz to 891 MHz 824 MHz to 891 MHz I channel 30kHz 30kHz bandwidth channels 21 cc1395

ve

21 cc

ı

395

ve

conversations per 1 3 or 6 channel

subscriber 40 to 50 conversations per 125 to 300 conversations per

capacity cell cell

TXIRCV type continuous time shared bursts

': carrier type constant phase variable constant frequency variable

frequency phase

ımbile/base mobile slaved to base authority shared

relationship cooperatively

privacy poor ~ _{better-easily scrambled}

"

noise immunity poor high

•

.

r.wd detection _{ESN plus optional password ESN plus optional password}

1.8.1. Time Division Multiple Access (TDMA)

North American digital cellular (NADC) is called DAMPS and TDMA. Because S preceded digital cellular systems, DAMPS uses the same setup protocols as

maJog AMPS. TDMA has the following characteristics:

54 standard specifiestraffic on digital voice channels

· · · implementationtriples the calling capacity of AMPS systems

<ııpacity improvements of 6 to 15 times that of AMPS are possible blocks of spectrum in 800 MHz and 1900 MHz are used transmissionsare digital

ıMAfFDMAapplication 7. 3 callers per radio carrier {6 callers on half rate later),

mnvvtino 3 times the AMPS capacity

IDMA is one of several technologies used in wireless communications. TOMA ~ each call with time slots so that several calls can occupy one bandwidth. Each is assigned a specific time slot. In some cellular systems, digital packets of

iı6Jımıtion are sent during each time slot and reassembled by the receiving equipment

the original voice components. TOMA uses the same frequency band and channel

4caions as AMPS. Like NAMPS, TOMA provides three to six time channels in the bandwidth as a single AMPS channel. Unlike NAMPS, digital systems have the

•

to compress the spectrum used to transmit voice information by compressing idle .,

and redundancy of normal speech. TDMA is the digital standard and has 30-k:Hz

•

•

Using digital voice encoders, TOMA is able to use up to six channels in the bandwidth where AMPS uses one channel.

~ Extended Time Division Multiple Access (E-TDMA)

E-TOMA standard claims a capacity of fifteen times that of analog cellular

a

ıs This capacity is achieved by compressing quiet time during conversations. E­ divides the finite number of cellular frequencies into more time slots than

~

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-e _.,· '•· • ,:/... ,

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,' :.;·....:. .• f ' 1·• ~.J~· 'f: • • ,·'t ,• I\, ı ,. / (: ....~·, ,."·,· > ' ı:,;-. ~"h ',~.p .• ,.:~~{ ~ .N., .•• , •;_..-ıt"; -~·:'....·

,·

\ '

.

Cellular Communication

1.8.3. Fixed Wireless Access (FWA)

FWA is a radio-based local exchange service in which telephone Service is provided by common carriers ( Figure1.9). It is primarily a rural application-that is, it reduces the cost of conventional wireline, FWA extends telephone service to rural areas by replacing a wireline local loop with radio communications. Other labels for wireless .-:cess include fixed loop, fixed radio access, wireless telephony, radio loop, fixed

C

· less, radio access, and Ionica. FWA systems employ TDMA or CDMA access technologies.

Figure ı9 Fixed Wireles~Access

•••••• Personal Communications Service (PCS)

••

future of telecommunications includes PCS. PCS at 1900 MHz (PCS 1900) is -.urth American implementation of digital cellular system (DCS) 1800 (GSM). Trial

Wwoı:ks were operational in the United States by 1993, and in 1994 the Federal

C wnrications Commission (FCC) began spectrum auctions. As of 1995, the FCC commercial licenses. In the PCS frequency spectrum, the operator's

1 wized frequency block contains a definite number of channels. The frequency plan

b

specific channels to specific cells, following a reuse pattern that restarts with cell. The uplink and downlink bands are paired mirror images. As with AMPS,

' r •

channel number implies one uplink and one downlink: frequency (e.g., Channel 512 =

50.2-MHz uplink paired with 1930.2-MHz downlink:).

S. Code Division Multiple Access (CDMA)

CDMA is a digital air interface standard, claiming 8 to 15 times the capacity of g. It employs a commercial adaptation of military, spread-spectrum, single­ ımeband technology. Based on spread spectrum theory, it is essentially the same as

· füıe service-the primary difference is that access to the local exchange carrier

C) is provided via wireless phone. Because users are isolated by code, they can the same carrier frequency, eliminating the frequency reuse problem encountered

AMPS and DAMPS. Every CDMA cell site can use the same 1.25-MHz band, so

respect to clusters, n = 1. This greatly simplifies frequency plannirtg in a fully '-U'M.A environment.

is an interference-limited system. Unlike AMPS/TDMA, CDMA has a soft

« a city limit; however, each user is a noise source on the shared channel and the noise ıi,oıed by users accumulates. This creates a practical limit to how many users a

J o will sustain. Mobiles that transmit excessive power increase interference to other

• n,;ı.

s For CDMA, precise power control of mobiles is critical in maximizing the

L o's capacity and increasing battery life of the mobiles. The goal is to keep each •I l at the absolute minimum power level that is necessary to ensure acceptable mıicc quality. Ideally, the power received at the base station from each mobile should

(minimumsignal to interference).

I

How cell phones works

2. HOW CELL PHONES WORKS 2.1. Introduction

Millions of people in the United States and around the world use cellular phones. They are such great gadgets with a cell phone; you can talk to anyone on the planet from just about anywhere as shown in the figure 2.1 a digital cell phone from nokia

I .•fl.;''

Figure 2.1 A digital cell phone from Nokia

We will be starting to explain how a cell phone works? What makes it different from a regular phone? What do all those confusing terms like PCS, GSM, CDMA and TDMA mean? In this chapter ot: we will discuss the technology behind cell phones.

2.2. The Cell Approach

One of the most interesting things about a cell phone is that it is really a radio an extremely sophisticated radio.sbut a radio nonetheless. The telephone was invented by Alexander Graham Bell in 1876, and wireless communication can trace its roots to the invention of the radio in 1894 by a young Italian named Guglielmo Marconi. It was only natural that these two great technologies would eventually be combined. In the dark ages before cell phones, people who really needed mobile communications ability installed radiotelephones in their cars. In the radiotelephone system, there was one central antenna tower per city, and perhaps 25 channels available on that tower. This central antenna meant that the phone in your car needed a powerful transmitter big enough to transmit 40 or 50 miles. It also meant that not many people could use radiotelephones there just were not enough channels. The genius of the cellular system is the division of a city into small cells. This allows extensive frequency reuse across a

city, so that millions of people can use cell phones simultaneously. In a typical analog cell phone system in the United States, the cell phone carrier receives about 800 frequencies to use across the city. The carrier chops up the city into cells. Each cell is typically sized at about 10 square ıniles (26 square kilometers). Cells are normally thought of, as hexagons on a big hexagonal grid. Each cell has a base station that consists of a tower and a small building containing the radio equipment. A single cell in an analog system uses one-seventh of the available duplex voice channels. That is, one cell, plus the six cells around it on the hexagonal grid, are each using one-seventh of the available channels so that each cell has a unique set of frequencies and there are no collisions:

• A cell phone carrier typically gets 832 radio frequencies to use in a city.

• Each cell phone uses two frequencies per call a duplex channel so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels.

• Therefore, each cell has 56 or so voice channels available.

In other words, in any cell, 56 people can be talking on their cell phones at one time. With digital transmitter methods, the number of available channels increases. For example, a TOMA-based digital system can carry three times as many calls as an analog system, so each cell would have about 168 channels available. Cell phones have low­ power transmitters in them. Many cell phones have two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts). The base station is also transmitting at low power. Low-power transmitters have two advantages:

• The transmissions of a base station and the phones within its cell do not make it

•

•

very far outside that cell. Therefore, in the figure above, both of the purple cells can reuse the same 56 frequencies. The same frequencies can be reused extensively across the city.

• The power consumption of the cell phone, which is normally battery-operated, is relatively low. Low power means small batteries, and this is what has made handheld cellular phones possible.

The cellular approach requires a large number of base stations in a city of any size. A typical large city can have hundreds of towers. But because so many people are using

How cell phones works

cell phones; costs remain low per user. Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO). This office handles all of the phone connections to the normal land-based phone system, and controls all of the base stations in the

2.3. Cell Phones Codes

An AMP specifies several identification codes for each mobile station. The mobile identification number (MIN) is a ten-digit telephone number, stored in a 34-bit binary representation. In the United States, this number has the same format as a conventional telephone number. The first three digits comprise the area code associated with the subscriber's home service area. This is followed by a seven-digit telephone number consisting of an exchange number (three digits) and a subscriber number (four digits). The exchange number is assigned to the cellular operating company. When a subscriber changes operating companies, it is necessary to change cellular phone numbers. In contrast to U.S. practice many countries assign special prefixes (corresponding to area code) exclusively to mobile telephone numbers. This practice makes it possible for callers to distinguish calls to mobile telephones from calls to conventional telephones.

Another identification code is a 32-bit electronic serial number (FSN) assigned permanently to each terminal. As a permanent characteristic of a physical unit, the ESN is similar to the engine number of a car. The MIN is analogous to the car's registration number, which, in the United States, changes when the car changes owners, or when the owner moves to a different state. A third identification code is the 4-bit station class mark (SCM), which describes the capabilities of the terminal. Station class marks indi­ cate whether the terminal has" access to all 832 AMPS channels or whether it is an old model with only 666 channels. Another prop

7

rty conveyed by the SCM is the maximum radiated power of the terminal. This could be either 600 mW or

4

W. As the AMPS

•

system evolves, the industry specifies new station class marks to identify mobile stations with special properties that influencenetwork

Control operations.

The system identifier (SID) is an important l-bit code stored in all base stations and all mobile Stations. In the United States, the Federal Communications Commission issues an SID to an operating company when it issues a license to offer service in a specific area. System is AMPS terminology for cellular operations provided by one company in a specific area. Thus, each base station is part of a system. In many places

,there is one NTSO per system .however, to or more systems with relatively small numbers of subscribers can share a single MTSO. Conversely, large system is likely to operate with two or more MTSOs.

Each mobile station stores the identifier of the system that administers its subscription. This is the home system of the terminal. When the mobile its subscription. This is the home system of the terminal. When the mobile station performs an initialization procedure, it compares its own SID with the SID broadcast by the local cell site. Identical SIDs indicate that the mobile station is using its home system .if the SIDs are not identical ,the mobile station is a roamer in another system. in this event, the terminals indicates, on its display, that its in roaming area. This alerts the subscriber to the possibilityof incurring special roaming charges

In addition to the SID assigned by regulatory authorities to the each base station, the local operating company assigns two identifiers, the digital color code(DDC) and the supervisory audio tone (SAT) ,which help mobile station distinguish neighboring base station from one another. The SAT assigned to a base station is one of three analog sine waves. Neighboring base stations operating with different SATs. The 2-bit digital color code serves a similarpurpose.

2.4. From Cell To Cell

All cell phones have special codes associated with them. These codes are used to identify the phone, the phone's owner and the service provider.

Let's say you have a cell phone, you turned it on, and someone tries to call you. Here is what happens to the call:

"'

• When you first power up the phone, it listens for an SID (see sidebar) on the control channel. The control channel is a special frequency that the phone and

•

base station use to talk to one another about things like call set-up and channel changing. If the phone cannot find any control channels to listen to, it knows it is out of range, and displays a "no service" message.

• When it receives the SID, the phone compares it to the SID programmed into the phone. If the SIDs matches, the phone knows that the cell it is communicating with is part of its home system.

• Along with the SID, the phone also transmits a registration request, and the MTSO keeps track of your phone's location in a database -- this way, the MTSO knows which cell you are in when it wants to ring your phone.

How cell phones works

• The MTSO gets the call, and it tries to find you. It looks in its database to see which cell you are in.

• The MTSO picks a frequency pair that your phone will use in that cell to take the call.

• The MTSO communicates with your phone over the control channel to tell it what frequencies to use, and once your phone and the tower switch on those :frequencies,the call is connected. You are talking by two-way radio to a friend! • As you move toward the edge of your cell, your cell's base station will note that

your signal strength is diminishing. Meanwhile, the base station in the cell you are moving toward (which is listening and measuring signal strength on all frequencies, not just its own one-seventh) will be able to see your phone's signal strength increasing. The two base stations coordinate themselves through the MTSO, and at some point, your phone gets a signal on a control channel telling it to change frequencies. This hand off switches your phone to the new cell.

2.5. Roaming

if the SID on the control channel does not match the SID programmed into your phone, then the phone knows it is roaming. The MTSO of the cell that you are roaming in contacts the MTSO of your home system, which then checks its database, to confirm that the SID of the phone you are using is valid. Your home system verifies your phone to the local MTSO, which then tracks your phone as you move through its cells. And thing is that all of this happens within seconds.

2.6. Cell Phone And CBS

A good way to understand the sophistication.of a cell phone is to•. compare it to a CB radio or a walkie-talkie.

Simplex and Duplex: Both walkie-talkies and CB radios are simplex devices. That is, two people communicating on a CB radio use the same frequency, so only one person can talk at a time as shown in the figure 2.2. A cell phone is a duplex device. That means that you use one frequency for talking and a second, separate :frequencyfor listening. Both people on the call can talk at once as shown in the figure 2.3. Channels: A walkie-talkie typically has one channel, and a CB radio has 40 channels. A typical cell phone can communicate on 1,664 channels or more.

Range: A walkie-talkie can transmit about one mile using a 0.25-watt transmitter. A CB radio, because it has much higher power, can transmit about five miles using a 5-watt transmitter. Cell phones operate within cells, and they can switch cells as they move around. Cells give cell phones incredible range. Someone using a cell phone can drive hundreds of miles and maintain a conversation the entire time because of the cellular approach.

Figure 2.2. In simplexradio, both transmitters use the same frequency. Only one party can

talk at a time.

•

re 2.3 In duplex radio, the two transmitters use different frequencies, so both parties can

How cell phones works

2. 7. Advance Mobile Phone System (AMPS)

In 1983, the analog cell phone standard called AMPS (Advanced Mobile Phone System) was approved by the FCC and first used in Chicago. AMPS use a range of frequencies between 824 MHz and 894 MHz for analog cell phones. In order to encourage competition and keep prices low, the U. S. government required the presence of two carriers in every market, known as A and B carriers. One of the carriers was normally the local exchange carrier (LEC), a fancy way of saying the local phone company.

Carriers A and Bis each assigned 832 frequencies: 790 for voice and another 42 for data. A pair of frequencies (one for transmit and one for receive) is used to create one channel. The frequencies used in analog voice channels are typically 30 kHz wide. The reason that 30 kHz was chosen as the standard size is because it gives you voice quality comparable to a wired telephone.

The transmit and receive frequencies of each voice channel are separated by 45 MHz to keep them from interfering with each other. Each carrier has 395 voice channels, as well as 21 data channels to use for housekeeping activities like registration, paging, etc. A version of AMPS known as Narrowband Advanced Mobile Phone Service (NA.MPS) incorporates some digital technology to allow the system to carry about three times as many calls as the original version. Even though it uses digital technology, it is still considered analog. AMPS and NA.MPS only operate in the 800 MHz band and do not offer many of the features common in digital cellular service such as e-mail and Web browsing.

2.8. Analog Comes Digital

Digital cell phones use the same radio technology as analog phones but in a different way. Analog systems do not fully utilize the signal between the phone and the cellular network. Analog signals cannot be compressed and manipulated as easily as a true digital signal. The same reasoning applies to many cable companies that are going to digital so they can fit more channels within a given bandwidth. Digital phones convert your voice into binary information (ls and Os) and then compress it. This compression allows between three and ten cell phone calls to occupy the space of asingle analog cell phone voice call. Many digital cellular systems rely on Frequency Shift Keying (FSK)

to send data back and forth over AMPS. FSK uses two frequencies, one for "1 "sand the other for "O"s, alternating rapidly between the two to send digital information between the cell tower and the phone. Clever modulation and encoding schemes are required to convert the analog information to digital, compress it and convert it back again while maintaining an acceptable level of voice quality. All this means that digital cell phones have to contain a lot of processing power.

2.9. Cellular Access Technologies

There is three common technologies used by cell phone networks for transmitting information:

1. Frequency Division Multiple Access (FDMA) 2. Time Division Multiple Access (TDMA) 3. Code Division Multiple Access (CDMA)

The first word tells you what the access method is and the second word, division, lets you know that it splits calls based on that access method.

• FDMA puts each call on a separate frequency.

• TDMA assigns each call a certain portion of time on a designated frequency. • CDMA gives a unique code to each call and spreads it over the available

frequencies.

"

The last part of each name is multiple accesses. This simply means that more than one user (multiple) can use (access) each cell."

•• 2.9.1. Frequency Division Multiple Access (FDMA)

Separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. Sends its signal at a different frequency within the available band. FDMA is used mainly for analog transmission as shown in the :fıgure2.4. While it is certainly capable of carrying digital information, FDMA is not considered to be an efficientmethod for digital transmission.

How cell phones works

0200() HowStuff_,.., FDMA

Figure2.4 In FDMA, each phone uses a different frequency.

2.9.2. Time Division Multiple Access (TDMA)

Do the Electronics Industry Alliance and the Teleconınıunications Industry Association use the access method for Interim Standard 54 (IS-54) and Interim Standard 136 (IS-136). Using TDMA, a narrow band that is 30 kHz wide and 6.7 milliseconds long is split time-wise into three time slots. Narrow band means channels in the traditional sense. Each conversation gets the radio for one-third of the time. This is possible because voice data that has been converted to digital information is compressed so that it takes up significantly less transmission space. Therefore, TDMA has three times the capacity of an analog system using the same number of channels. TDMA systems as shown in the figure 2.5 operate in either the 800 MHz (IS-54) or 1900 MHz (IS-136) frequency bands. ~

TDMA Is also used as the access technology for Global System for Mobile

•

•

communications (GSM) However, GSM implements TDMA in a somewhat different and incompatible way from IS- 136. Think of GSM and IS- 136 as two different operating systems that work on the same processor, like Windows and Linux both working on an Intel Pentium III. GSM systems use encryption to make phone calls more secure. GSM operates in the 900 MHz and 1800 MHz bands in Europe and Asia and in the 1900 MHz (sometimes referred to as 1.9 GHz) band in the United States. It is used in digital cellular and PCS-based systems. GSM is also the basis for Integrated Digital Enhanced Network (IDEN), a popular system introduced by Motorola and used by Nextel.

8.7MB

893.7MHz

•2ooottawStıtt&rh TDMA

Figure2.5 TDMA splits a frequency into time slots.

GSM is the international standard in Europe, Australia and much of Asia and Africa. In covered areas, cell-phone-users can buy one phone that will work anywhere else the standard is supported. To connect to the specific service providers in these different countries, GSM-users simply switch subscriber identification module (SIM) cards. SIM cards are small removable disks that slip in and out of GSM cell phones.

They store all the connection data and identification numbers you need to access a particular wireless service provider.

Unfortunately, the 1900 MHz GSM phones used in the United States are not compatible with the international system. If you live in the United States and need to have a cell phone access when you're overseas, the easiest thing to do is buy a GSM

@ıı

900MHzJ1800MHz cell phone for traveling.

"

. 2.9.3. Code Division Multiple Access (CDMA) •

Takes an entirely different approach from TDMA. CDMA, after digitizing data, spreads it out over the entire bandwidth it has available. Multiple calls are overlaid over each other on the channel, with each assigned a unique sequence code as shown in the figure 2.6. CDMA is a form of spread spectrum, which simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range.

How cell phones works

02000 How $Ml Wol!<ı CDMA

Figure 2.6 In CDMA, each phone's data has a unique code.

All of the users transmit in the same wide-band chunk of spectrum. Each user's signal is spread over the entire bandwidth by a unique spreading code. At the receiver, that same unique code is used to recover the signal. Because CDMA systems need to put an accurate time stamp on each piece of a signal, it references the GPS system for this information. Between eight and 1 O separate calls can be carried in the same channel space as one analog AMPS call. CDMA technology is the basis for Interim Standard 95 (IS-95) and operates in both the 800 MHz and 1900 MHz frequency bands. Ideally, TDMA and CDMA are transparent to each other. In practice, high power CDMA signals will raise the noise floor for TDMA receivers, and high power TDMA signals can cause overloading and jamming of CDMA receivers.

2.10. The Difference Between Cellular And PCs

Personal Communications Services (PCS) is a wireless phone service very similar to cellular phone service with an emphasis onpersonal service and extended mobility. The term "PCS" is often used in place of digital cellular, but true PCS means that other services like paging, caller ID and e-mail are bundled into the service.

While cellular was originally created for use in cars, PCS was designed from the ground up for greater user mobility. PCS has smaller cells and therefore requires a larger number of antennas to cover a geographic area. PCS phones use frequencies between 1.85 and 1.99 gig hertz (1850 MHz - 1990 MHz).

Technically, cellular systems in the United States operate in the 824-894 megahertz (MHz) frequency bands; PCS operates in the 1850-1990 MHz bands. And while it is based on TDMA, PCS has 200 kHz channel spacing and eight time slots instead of the typical 30 kHz channel spacing and three time slots found in digital cellular. Just like digital cellular, there are several incompatible standards using PCS technology. Two of the most popular are Cellular Digital Packet Data (CDPD) and GSM

2.11. Dual Band And Dual Mode

If you travel a lot, you will probably want to look for phones that offer dual band, dual mode or both. Lets take a look at each of these options.

• Dual Band: A phone that has dual band capability can switch frequencies. This means that it can operate in both the 800 and 1900 MHz bands. For example, a dual band TDMA phone could use TDMA services in either an 800 MHz or a

1900 MHz system.

• Dual Mode: In cell phones, mode refers to the type of transmission technology used. So, a phone that supported AMPS and TDMA could switch back and forth as needed. An important factor to look for is that one of the modes is AMPS. This gives you analog service if you are in an area that doesn't have digital support.

• Dual Band/Dual Mode: The best of both worlds allows you to switch between frequency bands and transmission modes as needed.

Phones that support thes~ options do changing bands or modes automatically. Usually the phone will have a default option set, such as 1900 MHz TDMA, and will try_,, to connect at that frequency with that technology first. If it supports dual bands, it will

•

switch to 800 MHz if it cannot connect at 1900 MHz. And if the phone supports more than one mode, it will try the digital mode(s) first, then switch to analog.

Sometimes you can even find Tri Mode phones. This term can be deceptive. It may mean that the phone supports two digital technologies, such as CDMA and TDMA, as well as analog. But it can also mean that it supports one digital technology in two bands and also offers analog support. A popular version of the TriMode type of phone for people who do a lot of international traveling has GSM service in the 900 MHz band for Europe and Asia, and the 1900 MHz band for the U.S. in addition to the analog service.

How cell phones works

2.12. Problems With Cell Phones

a cell phone, like any other consumer electronic device, can break. Here are some of the preventive measures you can take:

1. Generally, non-repairable internal corrosion of parts results if you get the phone wet or uses wet hands to push the buttons. Consider a protective case. If the phone does get wet, be sure it is totally dry before you switch it on to avoid damaging internal parts.

2. You can lessen the chance of dropping a phone or damaging the connectors if you use a belt-clip or a holster. The use of headsets really makes this consideration important.

3. Cracked display screens can happen when an overstuffed briefcase squeezes the cell phone.

4. Extreme heat in a car can damage the battery or the cell phone electronics. Extreme cold may cause a momentary loss of the screen display.

Analog cell phones suffer from a problem known as "cloning." A phone is "cloned" when someone steals its ID numbers and is able to make fraudulent calls on the owner's account. Here is how cloning occurs: When your phone makes a call, it transmits the ESN and MIN to the network at the beginning of the call. The MIN/ESN pair is a unique tag for your phone, and it is how the phone company knows whom to bill for the call. When your phone transmits its MIN/ESN pair, it is possible for nefarious sorts to listen (with a scanner) and capture the pair. With the right equipment, it is fairly easy to modify another phone so that it contains" your MIN/ESN pair, which allows the nefarious sort to make calls on your account. " ••

2.13. Inside A Cell Phone

On a "complexity per cubic inch" scale, cell phones are some of the most intricate devices people play with on a daily basis. Modem digital cell phones can process millions of calculations per second in order to compress and decompress the voice stream.

Figure 2.7 The various parts of a cell phone.

If you ever take a cell phone apart as shown in the figure 2.7, you will find that it contains just a few individualparts:

• An circuit board containing the brains of the phone • An antenna

• A liquid crystal display (LCD)

• A keyboard not unlike the one we saw in a TV remote control • A microphone

• A speaker • A battery

The circuit board is the heart of the system. Here is one from a typical Nokia digital phone:

••

••

a. The front of the circuit b. The back of the circuit

How cell phones works

In the figure2.8, there are several computer chips I will talk about what some of the individual chips do. The Analog-to-Digital and Digital-to-Analog conversion chips translate the outgoing audio signal from analog to digital and the incoming signal from digital back to analog. The Digital Signal Processor (DSP) is a highly customized processor designed to perform signal manipulationcalculations at high speed.

Figure 2.9 The Microprocessor.

The microprocessor as shown in the figure 2.9 handles all of the housekeeping chores for the keyboard and display, deals with command and control signaling with the base station, and also coordinates the rest of the :functions on the board. The RF and power section handles power management and recharging, and also deals with the hundreds of FM channels. Finally, the RF (Radio Frequency) amplifiers handle signals in and out of the antenna.

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il • • tıOWOıt

The display as shown in the figure 2.1O has grown considerably in size as the number of features in cell phones has increased. Most phones currently available offer built-in phone directories, calculators and even games. And many of the phones incorporate some type of PDA, or Web browser.

a. The flash memory card on the circuit board.

b. The flash memory card removed.

l!I

Figure 2.11 ROM and Flash Memory

In the figure 2.11 the ROM and flash memory chips provide storage for the phone's operating system and customizable features, such as the phone directory. Some phones store certain information, such as the SID and MIN codes, in internal flash memory while others use external cards that are similarto Smartmedia cards.

How cell phones works

Figure 12.2 The cell phone speaker,

microphone and battery backup.

Cell phones have such tiny speakers and microphones that it is incredible how well most of them reproduce sound. As shown in the figure2.12, the speaker is about the size of a dime and the microphone is no larger than the watch battery beside it. Speaking of the watch battery, this is used by the cell-phone's internal clock chip.

2.14. Cell Phones Tower

A cell phone tower as shown in the fıgure2.13 is typically a steel pole or lattice structure that rises hundreds of feet into the air. This cell phone tower along 1-85 near Greenville, S.C. is typical in the U.S.: This is a modem tower with three different cell phone providers riding on the same structure. In the figure 2.14 if you look at the base of the tower, you can see that each provider has its own equipment, and you can also see how little equipment is involved today (older towers often have small buildings at the base):

Figure 2.13 Modem Cell Phone Tower

•

How cell phones works

Figure 2.15 The Box Houses

As shown in the figure 2. 15The box houses the radio transmitters/receivers that let the tower communicate with the phones.

The radios connect with the antennae on the tower through a set of thick cables as shown in the Figure2.16

Figure 2.16 Using cables between radio antenna and tower 2.15. What They Can Do

Cell phones provide a way of staying in touch and having instant communication at your fingertips. With a cell phone, you can:

• Call your significant other to let them know that you are on your way home. • Contact the police or hospital if you have an emergency.

• Let the boss know that you are stuck in traffic and will be late for that big meeting.

• Provide a way for others to contact you if you are always on the go. • Call home or work to check your messages while on the road. • Store contact information (names and phone numbers).

• Make task or to-do lists (some models).

• Keep track and remind you of appointments (date book, calendar). • Use the built-in calculator for simple math.

• Send or receive e-mail (some models).

• Get information (news, entertainment, stock quotes) from the Internet. (Some models).

• Play simple games (some models).

• Integrate other devices such as PDAs, MP3 players and GPS receivers (some models).

2.16. Features

Here is a list of features that should be considered when looking for a cell phone:

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Service plan

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Mode

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Battery type

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Display

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Included functions

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Special Features

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Size ~

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Price •

2.16.1. Service Plan

Before you set your sights on a particular make or model of cell phone, you should decide on the service plan that interests you. Otherwise, you could find that the phone you want is not supported by the plan you need. We will go in depth about this subject in a dedicated article on "How Cell Phone Service Plans Work."

How cell phones works

2.16.2. Mode

Are you looking for analog or digital? Do you prefer PCS or cellular? TOMA or CDMA? If you have read the How They Work section, then you know what each of these terms mean. Look for dual mode/dual band phones if you travel a lot.

2.16.3. Battery Type

Cell phones use two main battery technologies:

• NiMH (Nickel Metal Hydride) - high capacity battery that provides extra power for extended use

• Li-ion (Lithium Ion) - has a lot of power in a lightweight package but usually costs more than NiMH batteries

Note both the talk time and standby time when comparing phones. Also, check to see how long the battery takes to recharge and whether a rapid charger is available. Most cell phone batteries are removable, but some of the smaller models have a built-in battery instead.

2.16.4. Display

All cell phones have LCD displays, but the specific features of the display can vary:

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Size - A large multi-line display is typically more expensive but necessary if you plan to use the phone for wireless Internet.

Colors vs. monochrome - Most cell phones have monochrome displays (16

•

grays), but a few are beginning to appear that have color. Cell phones with color

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'

screens need more memory and tend to be more expensive. •

Reflective or backlit - Almost all cell phones have backlit screens, which are good for low light conditions.

2.16.5. Include Function

Most premium phones offer all of these features while more economical phones may only have a few:

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Phone Directory

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Clock

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Calculator

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Games

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Personalized/custom sounds

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Appointment Reminder/Calendar

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Incoming number storage

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Automatic redial

• Last number recall

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Mute/hold button

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One touch dialing/speed dialing

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Vibrate mode

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Lock/Alarm

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Call forwarding

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Multiparty calls

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E-mail/text messaging

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Minibrowser 2.16.6. Special Features

Some cell phones have special'features such as:

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Wireless Internet

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Hands-free Headset/speakerphone

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External volume/ringer control

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Rapid charger/built-in charger

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Car adapter

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Modem function

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PC synchronization

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PDA

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MP3 player

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SIM Card

3. SIM CARD

3.1. Introduction

The SIM card's basic functionality in wireless communications is subscriber authentication and roaming. Although such features may be achieved via a centralized intelligent network (IN) solution or a smarter handset, there are several key benefits that could not be realized without the use of a SIM card, which is external to a mobile handset. These benefits=-enhanced security, improved logistics, and new marketing opportunities-are key factors for effectively differentiating wireless service offerings. A sim card (subscriber identity module) or smart card is astandard card-sized plastic token within which a microchip has been embedded. This chip is the engine room of the smart card, and indeed is what makes it 'smart'. Smart card chips come in two broad varieties: memory-only chips, with storage space for data, and with a reasonable level of built-in security; and microprocessor chips which, in addition to memory, embody a processor controlled by a card operating system, with the ability to process data onboard, as well as carrying small programs capable of local execution. The main storage area in such cards is normally EEPROM (Electrically Erasable Programmable Read-Only Memory), which - subject to defined security constraints - can have its content updated, and which retains current contents when external power is removed. Newer smart card chips may also have maths co-processors integrated into the microprocessor chip, able to perform quite complex encryption routines relatively quickly.

A smart card is therefore characterised uniquely by its chip, with its ability to store ••

much more data (currently up to about 32,000 bytes) than is held on a magnetic stripe, all within an extremely secure environment. These security features built into smart card chips are amongst the most sophisticated of their type available in the commercial world. Data residing in the chip can be protected against external inspection or alteration, so effectively that the vital secret keys of the cryptographic systems used to protect the integrity and privacy of card-related communications can be held safely against all but the most sophisticated forms of attack. The ingenuity of the cryptographers further supplements the physical security of the chip, ensuring that penetrating one card's security does not compromise an entire card scheme.

It is because of these security and data storage features that smart cards are rapidly being embraced as the consumer token of choice in many areas of the public sector and commercial worlds. The Internet, in particular, is focussing the need for online identification and authentication between parties who cannot otherwise know or trust each other, and smart cards - coupled with effective cardholder verification techniques - are believed to be the most efficient and portable way of enabling the new world of e- trade. is the key requirement to facilitate universal consumer acceptability: the ability of a card function developed by one organisation to be used without difficulty in schemes owned and operated by many organisations. So it is that the current world population of smart cards of some I. 7 billion is set to increase to 4 billion or more cards within the next 3-4 years.

3.2.

Smart card functions

Smart cards are being deployed in most sectors of the public and private marketplaces. Single-function cards are being used for payphone telephony, digital mobile telephony (these 'cards' do not in one aspect conform to the basic definition of a smart card, i.e. credit card-sized), the credit and debit functions of :financial institutions, retail loyalty schemes, corporate staff systems, subscription TV operations, mass transit ticketing schemes and many more. With the advent of multi-application cards capable of carrying data relating to several functions, more complex schemes are being developed, particularly by cities for their citizens and by central Governments for their residents. In most of these schemes, simple data structures are held and updated within cards, normally comprising personal information about the cardholder and his or her

8

accounting relationship with the card and application issuer, together with transactional data relating to the particular function. Central processing systems often mirror this

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data, having collected it through a polling mechanism from the terminals that accept the particular cards and enable them to participate in the related transactions.

Most smart card schemes utilise one or more generic functions, this being one of several advantages offered by smart technology. Another advantage of smart cards is that these functions are frequently associated with oflline operations, i.e. functions performed without immediate access to the central system. The generic functions of cards include general transaction-based storage, storage of kernel personal data and